Unregistering Sony devices from PSN Account

[sj33]

From what I understand, you can only have 5 devices (PS3, PSP, Vita) registered to a PSN account. If you wish to unregister that device, you need to go to the website and connect the PSP or Vita that you want to unregister via USB.

This sounds all well and good, but I have a bit of a snag. I have actually maxed out my registered devices list, and a couple of the PSP devices currently registered to the account cannot be unregistered due to the fact that they no longer exist (long story, but these are dead PSPs). I registered my Vita by unregistering my PSP, but is there any way of removing these redundant devices from the registreation list without having to physically connect them?

[gIzzE]

Is there not a failsafe where you can unregister all devices at once, and then add the ones you want again?

This is what you do on macs.